The present invention relates to instruments for chemical and biological analyses employing surface plasmon resonance and, in particular, to an instrument having an improved light path that may be easily adjusted.
In surface plasmon resonance, a sensor comprised of a thin metallic film is illuminated by light of an appropriate wavelength and angle of incidence on a “reflecting” side of the film. The energy from the light couples to electrons of the metal of the film creating a resonant condition (surface plasmon resonance) that is highly sensitive to surface conditions on a “sensing” side of the film opposite the side that is illuminated.
Probe molecules may be attached to the sensing side of the metallic film to selectively bind with target molecules in a solution to be analyzed. This binding, through the agency of the electron resonance in the film, causes a drop in reflectance of the reflecting side of the film. Detection of the decrease in reflected light thus provides a sensitive measurement of the binding of target molecules to the probe molecules, in turn providing a sensitive indication of the presence of target molecules in the solution being analyzed.
By placing a variety of different probe molecules on the sensing surface of the film, many different target molecules may be rapidly assessed. Importantly, the target molecules need not be labeled with fluorescent dye or the like prior to analysis.
Current surface plasmon resonance (SPR) equipment can be bulky and difficult to use. Adjustment of the optical system may require separate movement of an analyzing camera and/or light source and possible rotation of the sensing surface. Typically, the sensing surface is oriented vertically, which allows ready access to the optical system for such adjustment, but this vertical orientation can cause problems sealing the flow cells holding the solution to be analyzed against the sensing surface. SPR equipment with a horizontal sensing surface has been constructed to improve access to the sensing surface and improved sealing of the flow cell. The resulting displacement of the camera and light source below the sensing surface, however, complicates adjustment of the camera and light source and undesirably increases the overall height and bulk of the instrument.